A fuel cell battery is a stack of elementary cells in which an electrochemical reaction takes place between reactive products that are gradually introduced as the reaction consumes them. The fuel, which is hydrogen in the case of a hydrogen fuel cell battery, is brought into contact with the anode; the oxidant, oxygen or air for a hydrogen fuel cell battery, is brought into contact with the cathode. The anode and cathode are separated by an electrolyte, possibly a solid membrane, that is permeable to certain of the constituents of the reaction but not all. The reaction is subdivided into two half reactions (an oxidation and a reduction), which take place, on the one hand, at the anode/electrolyte interface, and on the other hand, at the cathode/electrolyte interface. In practice, the solid electrolyte is a membrane that is permeable to hydrogen ions H+ but not to molecular dihydrogen H2 or electrons. The reduction reaction at the anode is oxidation of hydrogen producing H+ ions, which pass through the membrane, and electrons, which are collected by the anode; at the cathode these ions participate in the reduction of oxygen, requiring electrons and producing water, heat also being given off.
The stack of cells is only the location of the reaction: the reactants must be supplied thereto, and products and non-reactive species must be evacuated, just like the heat produced. Lastly, the cells are electrically connected in series to one another, the anode of one cell being connected to the cathode of the adjacent cell; at the ends of the stack of cells, on one side an anode is connected to a negative terminal in order to evacuate electrons, and on another side a cathode is connected to a positive terminal. An external circuit is connected to these terminals. Electrons flow from the anode to the cathode via the external circuit thus powered by the battery as the electrochemical reaction progresses.
Conventional fuel cell batteries comprising stacked cells comprise a superposition of what are called bipolar plates, between which are placed assemblies comprising, at the same time, an electrolytic membrane and an electrode on each side of the membrane. The bipolar plates, optionally associated with sealing joints having a particular configuration, serve to collect electrical current and to distribute the reactant gases (hydrogen and air, or hydrogen and oxygen) to the membrane, on the appropriate side of the membrane: hydrogen on the anode side, air or oxygen on the cathode side. They comprise distribution channels facing the anodes and others facing the cathodes. They may also comprise cooling channels. On their periphery, the plates are pierced with apertures serving to deliver the reactant gases, and apertures serving to evacuate the products of the reaction. The apertures for delivering reactant gas form, via the superposition of plates in intimate contact with one another, manifolds for supplying reactant gas. The evacuation apertures form, in the same way, manifolds for evacuating the products of the reaction. Sealing joints are provided so that the fluids remain confined in these manifolds, but the design of the bipolar plates and/or the sealing joints is such that passages are formed in the manifolds in the locations where it is desired to distribute the fluid to a cell so that the fluid penetrates into the cell, on the desired side, without crossing to the other side. These passages direct the reactant gases to the cell via distribution channels formed in the plates, which distribute the gas as uniformly as possible over the electrolytic membrane.
The same applies to the reaction products, the plates and joints being designed in order to allow the reaction products to be gathered and evacuated, on the anode side and/or the cathode side, to the evacuation manifold.
Thus, the supply manifold for supplying a conventional cell with hydrogen consists of a stack of plates and joints designed such that the hydrogen can spread in the cells on the anode side, but absolutely not on the cathode side. The opposite is true for the supply manifold supplying air or oxygen.
At the end of the stack these apertures formed in the plates are respectively connected to a respective supply duct for each reactive product and an evacuation duct for the products of the reaction.
The stack of cells is clamped tight by rods passing through all the bipolar plates and membranes. The exerted pressure seals the cells relative to one another, and creates a seal between the anode side and the cathode side of the cell.
In the prior art, structures have been proposed in which the bipolar plates are cut in a complex way in order to define both the fluid distributing channels and the apertures that, in the superposition of plates, form the supply and evacuation manifolds. The pressure exerted between the plates when they are clamped tightly against one another creates the desired seal in the locations where communication between a manifold and a cell must be prevented (for example there must be no communication between a hydrogen supply manifold and the cathode side of the cell, and no communication between an air supply manifold and the anode side). In the locations where communication must be possible, notches are provided in the bipolar plate.
Patent FR 2 887 689 describes such bipolar plates, which may be made of stamped metal or of other materials such as graphite-filled polymer. But it is not possible in this case for the plates to take the form of a single sheet.
Structures have also been proposed in which a suitably cut plate providing a peripheral seal maintains a seal everywhere where it must be maintained but allows the reactive gas to pass from the manifold into a cell in the locations where it needs to pass. The joint is planar on the electrolytic-membrane side in order to support the latter and it has a more sophisticated shape on the bipolar-plate side. The distribution channels that run from the manifold to the active surface of the membrane may be produced in the seal.
U.S. Pat. No. 5,482,792 describes such a structure. Uniform gas distribution may then be obtained via a foam plate clamped between the peripheral seal and the bipolar plate. The parts of the stack are complex to produce, their cost is high, and they are large in thickness, thereby adversely affecting the compactness of the battery. Lastly, because it must neither be too pliable (in order to allow the channels to be produced) nor too rigid (for the sealing function), the plate forming the complex seal is difficult to produce.
In the above two examples, different bipolar and joint plates are required for the anode side and cathode side of the cells, thereby increasing manufacturing cost.
U.S. Pat. No. 5,532,073 describes injection washers the configuration of which is such that they could not be applied against electrolytic membranes without damaging them.
Publication US 2010/0209800 describes flat joints welded to plates, which joints could not be applied against a flexible electrolytic membrane without damaging it.